Ribbed buoy



FIG. 1 is a perspective front and right side view of a ribbed buoy, showing my new design;

FIG. 2 is a right side view thereof, the left side view being a mirror image;

FIG. 3 is a front view thereof;

FIG. 4 is a top view thereof, the bottom view being a mirror image; and,

FIG. 5 is a rear view thereof. 

The ornamental design for a ribbed buoy, as shown and described. 